1. Field of the Invention
The field of this invention is that of generating a DC signal having an amplitude related to the amplitude of a noisy AC signal.
2. Description of the Prior Art
In constructing feedback control systems it is sometimes necessary to generate a direct current feedback signal that is proportional to an alternating current signal developed by a transducer. One method utilized for generating such a feedback signal has been to full-wave rectify the AC signal and then filter this rectified signal. A disadvantage of this method is that if the signal is filtered sufficiently to smooth the pulsating DC, a long time constant filter must be employed. This generates a long time delay between the AC signal and the signal that is fed back as a control signal. For many applications this delay is unacceptable. Because of the long time constant, however, this method is relatively insensitive to noise or distortion of the AC signal.
A second method that has been used is to full-wave rectify the AC signal and then follow this rectifier with a peak detector. A signal is maintained at the output of the peak detector equal to the peak amplitude of the last half cycle of the alternating current signal. This method has less time delay than the filtered method but it is very sensitive to noise and distortion in the AC signal, since any ripple occurring at the peak of the AC signal will be recognized as signal.